1. Open image with colors of interest
2. Use the smudge tool to blur the original image detail
3. Use the Elipse selection tool for smooth "river pebble" or the Lasso tool for a more irregular "stone"
4. New Layer via Copy
5. Turn off the background layer to visualize only the "pebble"
6. Right click in the new layer window and open the blending options.
7. Adjust bevel/emboss and drop shadow to your liking
8. Move the newly created layer into other images and resize as needed.

I moved the pebble to a new area of the image and erased some of the background layer to increase the screen shot demonstration visibility.